DevTools: Enable JS Capability for inspector_main

Presently, the isNodeJS() method uses '===' operator
which evaluates to true only for JS Capability. This
check fails for inspector_main target as multiple
capabilities are set for it.
As a result, source maps doesn't get applied for
inspector_main because the isNodeJS() check fails
and prevents prefixing of "file://" to sourceMapURL
as a consequence, leading to the source maps resource
not being served.

In this patch, we set only the JS Capability for
inspector_main if the 'v8only' parameter in the URL
is set to true.

Bug: 846642
Change-Id: I96a01f3b984bf552c89c873d10f3bf0b5ecd67c8
Reviewed-on: https://chromium-review.googlesource.com/1095064
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568539}

AUTHORS

@@ -269,6 +269,7 @@ Gajendra Singh <wxjg68@motorola.com>
 Ganesh Borle <ganesh.borle@samsung.com>
 Gao Chun <chun.gao@intel.com>
 Gao Chun <gaochun.dev@gmail.com>
+Gautham Banasandra <gautham.bangalore@gmail.com>
 George Adams <geoada@amazon.com>
 George Joseph <kottackal.george@gmail.com>
 George Liaskos <geo.liaskos@gmail.com>

third_party/blink/renderer/devtools/front_end/inspector_main/InspectorMain.js

@@ -41,6 +41,8 @@ InspectorMain.InspectorMain = class extends Common.Object {
    * @return {number}
    */
   _capabilitiesForMainTarget() {
+    if (Runtime.queryParam('v8only'))
+      return SDK.Target.Capability.JS;
     return SDK.Target.Capability.Browser | SDK.Target.Capability.DOM | SDK.Target.Capability.DeviceEmulation |
         SDK.Target.Capability.Emulation | SDK.Target.Capability.Input | SDK.Target.Capability.JS |
         SDK.Target.Capability.Log | SDK.Target.Capability.Network | SDK.Target.Capability.ScreenCapture |